A cadre of congressional Republicans would like to defund Obamacare and would be willing to risk a government shutdown to make that happen. A leading voice in the Senate is Mike Lee of Utah. Lee says the law is so bad, even key Democratic allies don't like it.

"By a margin of two to one, Americans say Obamacare will make their family's health care situation worse, not better. Just 12 percent support the individual mandate. Doctors don't want it. Businesses oppose it. Unions say it's bad for workers," Lee wrote in an op-ed in USA Today.

That last group, the unions, caught our eye. Organized labor is one of the pillars of the Democratic Party and lobbied for passage of the Affordable Care Act.

Lee's office pointed us to a press release and a letter. The press release from United Union of Roofers, Waterproofers and Allied Workers called for "repeal or complete reform of President Obama's Affordable Care Act." The letter came from three of the larger unions in the country: the Teamsters, the United Food and Commercial Workers International Union, and UNITE HERE, which represents hotel workers. Those three unions sent a dire warning to the Democratic leaders in the House and Senate.

Why?

Many unions offer health insurance through unusual plans that allow large and small employers to buy coverage as a group, and some of the unions that are involved in these plans have big objections to the health care law.

Randy DeFrehn is executive director of the National Coordinating Committee for Multiemployer Plans, a sort of trade association for these insurance groups. DeFrehn said at least six unions have gone public with their objections to Obamacare. Behind the scenes, he said, the number is larger.

"Altogether, there are a dozen or more out there," DeFrehn said. "They don't all want to come out against the administration, but they are worried about the unintended consequences of the law."

One central problem with the law, in the unions' view, is the threat it poses to the kind of health insurance their members enjoy today. Just as there are different insurance companies, there are different union insurance plans, about 3,000.

These plans are often called Taft-Hartley plans after the federal labor law that created them. And here's the rub: The Affordable Care Act creates insurance exchanges that will present employers with a new alternative to the current union insurance.

"The unions think it will be cheaper for employers to drop out of the Taft-Hartley plans and go on the health exchange," said Paul Secunda, a labor law professor at Marquette University Law School. "This puts pressure on the unions who want to keep workers satisfied."

Another issue for unions is how the law treats part-time workers. While the law encourages employers to provide insurance, there are two primary escape clauses. Companies with fewer than 50 full-time workers face no requirement to offer it. And no employer need provide coverage to anyone working less than 30 hours each week.

Bottom line: Lee is right that some unions oppose the health care law. But the union community is not monolithic, and some large unions continue to support the Affordable Care Act as much as ever.